This invention relates to a pulse-motor driving apparatus used in an image communication apparatus capable of transmitting/receiving image data or copying an image.
As methods for controlling pulse-motor drive current (simply referred to as "drive current") in a conventional pulse-motor driver, mainly BIT control method and PWM control method are known. In the BIT control method, a control signal to control a drive current value of a motor-driver IC is a digital signal. The drive current value is controlled by a signal D/A converted from the digital signal. In the PWM control method, a control signal to control the motor-driver IC is a pulse-width modulation signal (PWM signal). The drive current value is controlled in accordance with a voltage level signal analog-converted from the PWM signal. One of these controls is performed to control a motor-driver current.
However, these conventional controls have the following problems. The BIT control executes the drive current control by D/A conversion. This provides excellent follow-up characteristic of the drive current value with respect to the control signal. However, delicate drive current control is difficult because the steps of current-control by the motor-driver IC are limited. This limits motor-drive torque control. Especially, when the drive speed slows down, as an appropriate torque cannot be obtained, there is a high probability that noise or out-of-synchronization may occur.
The PWM control, which executes drive current control by a voltage level, can perform very delicate drive current control. However, as the control signal is an analog signal, the change of current value has a transient phenomenon. As a result, follow-up characteristic of the drive signal with respect to the control signal becomes poor. Accordingly, if the motor drive speed is increased, the period required to obtain a desired current value of the drive signal is prolonged, which increases the possibility of noise or out-of synchronization.